In several industries (for example, the varnish, printing ink, paint, and lithography markets), multilayer systems are used in connection with a variety of substrates. In some instances, these systems contain acid-curable resins. Acid-curable resin compositions contain at least one component capable of acid-catalyzed polycondensation. These materials are familiar to those skilled in the art; they are produced industrially in large quantities with modifications to their material properties as appropriate for a great number of applications. In some instances, the materials cross-link to form coating layers. Acid-curable resin compositions can contain, for example, alkyd resins, melamine resins, urea resins, guanamine resins, phenolic resins, polyester resins, (meth)acrylic resins, polyvinyl resins, vinyl ethers, vinyl esters, styrene/substituted styrene resins, polyimide resins, epoxide resins, urethane resins, and mixtures thereof. Examples of mixtures include, but are not limited to, melamine/(meth)acrylic resins, melamine/polyester resins, melamine/alkyd resins, vinyl ether/(meth)acrylic resins, vinyl ether/substituted styrene resins, and the like. One example where multilayer systems are used is the microlithography or photolithography industry.
Photoresist compositions are used in microlithography processes for making miniaturized electronic components such as in the fabrication of computer chips and integrated circuits. Generally, in these processes, a thin coating of a film of a photoresist composition is first applied to a substrate material, such as silicon wafers used for making integrated circuits. The coated substrate is then baked to evaporate any solvent in the photoresist composition and to fix the coating onto the substrate. The baked and coated surface of the substrate is next subjected to an image-wise exposure to radiation. The radiation exposure causes a chemical transformation in the exposed areas of the coated surface. Visible light, ultraviolet (UV) light, electron beam and X-ray radiant energy are radiation types commonly used today in microlithographic processes. After this image-wise exposure, the coated substrate is treated with a developer solution to dissolve and remove either the radiation-exposed or the unexposed areas of the photoresist.
There are two types of photoresist compositions, negative-working and positive-working. When positive-working photoresist compositions are exposed image-wise to radiation, the areas of the photoresist composition exposed to the radiation become soluble in a developer solution while the unexposed areas of the photoresist coating remain relatively insoluble to such a solution. Thus, treatment of an exposed positive-working photoresist with a developer causes removal of the exposed areas of the photoresist coating and the formation of a positive image in the coating, thereby uncovering a desired portion of the underlying substrate surface on which the photoresist composition was deposited. In a negative-working photoresist the developer removes the portions that are not exposed.
The trend towards the miniaturization of semiconductor devices has led both to the use of new photoresists that are sensitive to lower and lower wavelengths of radiation, and also to the use of sophisticated multilevel systems to overcome difficulties associated with such miniaturization.
In these multilevel or multilayer systems, for example, the use of highly absorbing antireflective coatings in photolithography is a simpler approach to diminish the problems that result from back reflection of light from highly reflective substrates. A developable bottom antireflective coating is applied on the substrate and then a layer of photoresist is applied on top of the antireflective coating. The photoresist is exposed imagewise and developed. The developable bottom antireflective coating is also developable with the same aqueous alkaline developing solution as that used to typically develop the photoresist. Additionally, barrier coatings or top antireflective coatings or immersion protection coatings are also used in multilayer systems.
Often times, the formulations used in the coatings industries, are baked at temperatures above room temperature. The baking temperatures can vary, depending upon the type of coating applied and its desired use. In some instances, having a coating which contains a thermal acid generator with a low decomposition temperature, which in turn relates to a low baking temperature, is beneficial.